Advanced processing of CdTe pixel radiation detectors

Abstract

We report a fabrication process of pixel detectors made of bulk cadmium telluride (CdTe) crystals. Prior to processing, the quality and defect density in CdTe material was characterized by infrared (IR) spectroscopy. The semiconductor detector and Flip-Chip (FC) interconnection processing was carried out in the clean room premises of Micronova Nanofabrication Centre in Espoo, Finland. The chip scale processes consist of the aluminum oxide (Al 2 O 3 ) low temperature thermal Atomic Layer Deposition (ALD), titanium tungsten (TiW) metal sputtering depositions and an electroless Nickel growth. CdTe crystals with the size of 10 × 10 × 0.5 mm 3 were patterned with several photo-lithography techniques. In this study, gold (Au) was chosen as the material for the wettable Under Bump Metalization (UBM) pads. Indium (In) based solder bumps were grown on PSI46dig read out chips (ROC) having 4160 pixels within an area of 1 cm 2 . CdTe sensor and ROC were hybridized using a low temperature flip-chip (FC) interconnection technique. The In-Au cold weld bonding connections were successfully connecting both elements. After the processing the detector packages were wire bonded into associated read out electronics. The pixel detectors were tested at the premises of Finnish Radiation Safety Authority (STUK). During the measurement campaign, the modules were tested by exposure to a 137 Cs source of 1.5 TBq for 8 minutes. We detected at the room temperature a photopeak at 662 keV with about 2 % energy resolution.

AC-coupled n-in-p pixel detectors on MCz silicon with atomic layer deposition (ALD) grown thin film

“…Surface passivation with ALD-grown Al 2 O 3 can also be extended to other semiconductor detector materials, such as CdTe. [137] These may require quite different adaptations to the ALD process than high-resistivity silicon, such as film deposition at low temperature.…”

Cadmium Telluride X-ray pad detectors with different passivation dielectrics

“…Following dielectric deposition, the contact openings were created by wet etching for both passivation types. The fabrication process sequence is described in reference [25].…”

Electromigration and Polarization in Schottky Contacts CdTe Based Compounds

“…The distribution and the stability of the electric field in the CZT sample (S2) are studied by employing the Pockels effect technique and using equation (5). The profiles of the internal electric field during 80 minutes in the sample at 300K and bias 250 V are presented in Fig.…”

“…During the last decade Cadmium telluride (CdTe) based compounds have been extensively studied due to their wide range of applications [1][2][3][4][5][6][7][8]. In most of these applications, two metals contacts are deposited on CdTe and metal/semiconductor/metal structure (M-S-M) are formed.…”